88K5 350 tbi mostly stock. From manifolds back I'm wanting to go 3'' Y pipe 3'' single exhaust one high flow muffler? Is that enough back pressure ? O2 sensor is in the drivers side manifold. I read somewhere that the 3'' y pipe made a big difference over the stock one ? Will this negatively effect my ecu?
CK5
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Lets talk exhaust!
- Thread starter prolinews
- Start date
I honestly doubt the 3" will do much with manifolds. They are the real restriction in the system.
You don't want or need backpressure. Thread awhile back that covered that myth, but suffice it to say, backpressure is bad. But too big is as bad as too small as well, to an extent.
It may or may not affect the ECM. My expectation though, is that if the manifolds stay in place, and the O2 location doesn't move, flow differences in exhaust will be minimal, and won't affect fueling thus no ECM reprogramming would likely be necessary.
You don't want or need backpressure. Thread awhile back that covered that myth, but suffice it to say, backpressure is bad. But too big is as bad as too small as well, to an extent.
It may or may not affect the ECM. My expectation though, is that if the manifolds stay in place, and the O2 location doesn't move, flow differences in exhaust will be minimal, and won't affect fueling thus no ECM reprogramming would likely be necessary.
4xcrazy
3/4 ton status
2.5" pipes off the manifolds, 3" from the y-pipe back.
Actually, I asked a muffler shop for some 3" pipe from the cat back as replacement when I swapped in a new muffler, and they ended up having to stretch the pipe a little off the factory pipe stub coming off the cat I left on there to match the diameter.
Actually, I asked a muffler shop for some 3" pipe from the cat back as replacement when I swapped in a new muffler, and they ended up having to stretch the pipe a little off the factory pipe stub coming off the cat I left on there to match the diameter.
Eh, without some numbers I question exhaust diameter.
Flow numbers for a given diameter of pipe are known, but AFAIK the flow numbers for manifolds are not, and since exhaust cools and decreases in volume, the flow requirement for exhaust pipe isn't static in any case.
If one knew what the head exhaust gas temp was, and the exhaust temperature along varying points, an actual effective pipe diameter could be calculated.
As far as I can tell, most everyone now simply goes with what the minimum "fits all" size would be as far as CFM as an educated guess, and for most small blocks, 3" is it. Without headers, I really question the need for 3" unless it saves cost, because I doubt the gains are there. It should be needed with a cat which would bring exhaust gas temp way back up, but without a converter, pipe diameter for performance should decrease as you get further from the motor.
Flow numbers for a given diameter of pipe are known, but AFAIK the flow numbers for manifolds are not, and since exhaust cools and decreases in volume, the flow requirement for exhaust pipe isn't static in any case.
If one knew what the head exhaust gas temp was, and the exhaust temperature along varying points, an actual effective pipe diameter could be calculated.
As far as I can tell, most everyone now simply goes with what the minimum "fits all" size would be as far as CFM as an educated guess, and for most small blocks, 3" is it. Without headers, I really question the need for 3" unless it saves cost, because I doubt the gains are there. It should be needed with a cat which would bring exhaust gas temp way back up, but without a converter, pipe diameter for performance should decrease as you get further from the motor.
Nothing to do with EFI, the problem in general is that we've learned a lot about motors since GM designed the small block.
Only thing the ECM will care about is air/fuel mix at the O2 sensor. As long as you don't change the air/fuel ratio much, it's not going to care what you do to the exhaust.
But if you aren't changing the air/fuel ratio, your wasting your time, as that is the only way to make more power.
Edit: to clarify, air/fuel ratio changes come from modifying the exhaust IF the modifications increase flow and/or scavenging under the conditions your engine normally operates. An exhaust in one sense is like a garden hose...one restriction is all it takes. Nothing past the restriction will flow more. As an example, if the manifolds are your *sole* restriction then doing anything to the exhaust past the manifold won't make a difference. In our trucks of course, the bends weren't mandrel, the flat converter sucked, etc., so the LIKELIHOOD of poor performance due to exhaust design is likely, but not a given. It's near impossible to figure that out without simply strapping the truck to a dyno and changing one component at a time.
This is where the O2 sensor helps. If you go lean after an exhaust modification (actually any engine modification), you know you've gained power because your A/F mix has changed. That means your engine is ingesting more air. If you get the fuel back inline you will make more power. If you don't go lean, you've accomplished nothing. That's a pretty simple fact to understand.
The inverse of this is the import "tuner" syndrome. Look at the back of the majority of the fart-can equipped cars. If the "tip" is in proximity to the body, it will be covered in carbon. This would tell any halfway intelligent person that exhaust is no longer flowing through the exhaust, it is wafting, meaning velocity has been compromised, and more than likely, so has performance. As long as all you care about is looks and sound, that is fine of course.
Only thing the ECM will care about is air/fuel mix at the O2 sensor. As long as you don't change the air/fuel ratio much, it's not going to care what you do to the exhaust.
But if you aren't changing the air/fuel ratio, your wasting your time, as that is the only way to make more power.
Edit: to clarify, air/fuel ratio changes come from modifying the exhaust IF the modifications increase flow and/or scavenging under the conditions your engine normally operates. An exhaust in one sense is like a garden hose...one restriction is all it takes. Nothing past the restriction will flow more. As an example, if the manifolds are your *sole* restriction then doing anything to the exhaust past the manifold won't make a difference. In our trucks of course, the bends weren't mandrel, the flat converter sucked, etc., so the LIKELIHOOD of poor performance due to exhaust design is likely, but not a given. It's near impossible to figure that out without simply strapping the truck to a dyno and changing one component at a time.
This is where the O2 sensor helps. If you go lean after an exhaust modification (actually any engine modification), you know you've gained power because your A/F mix has changed. That means your engine is ingesting more air. If you get the fuel back inline you will make more power. If you don't go lean, you've accomplished nothing. That's a pretty simple fact to understand.
The inverse of this is the import "tuner" syndrome. Look at the back of the majority of the fart-can equipped cars. If the "tip" is in proximity to the body, it will be covered in carbon. This would tell any halfway intelligent person that exhaust is no longer flowing through the exhaust, it is wafting, meaning velocity has been compromised, and more than likely, so has performance. As long as all you care about is looks and sound, that is fine of course.
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I tend to agree that the manifold is probably your restriction point. I also think you should go ahead with your plan as is.
The whole goal of a custom exhaust is to remove restrictions. your plan is good
The whole goal of a custom exhaust is to remove restrictions. your plan is good
fyi go measure the y-pipe you got under there . lots of them were 3" @ the collector but necked down in the mid pipe to 2.5" . and if you still have a pancake / ball style cap swap it out for a newer style honeycomb MUCH better flowing cat .
and as said 2.5" to 3" collector . some like to use this http://www.summitracing.com/parts/flo-y250300/overview/ and have a shop build the y-pipe.
good set of shorty headers or long tubes work . but search here for what 2 or 3 part #'s fit our trucks with out hitting the shackles BAD .
and the tbi engine has a super tiny cam in it . read up on efi friendly cams o swap in and help . but you will need a chip done also . the efi section here has lots of good info .
and as said 2.5" to 3" collector . some like to use this http://www.summitracing.com/parts/flo-y250300/overview/ and have a shop build the y-pipe.
good set of shorty headers or long tubes work . but search here for what 2 or 3 part #'s fit our trucks with out hitting the shackles BAD .
and the tbi engine has a super tiny cam in it . read up on efi friendly cams o swap in and help . but you will need a chip done also . the efi section here has lots of good info .
